Hyperbranched structure grafting-based shrinkage reducing agent for UHPC (Ultra High Performance Polycarbonate) and preparation method of shrinkage reducing agent

Abstract

The invention discloses a hyperbranched structure grafting-based shrinkage reducing agent for UHPC (Ultra High Performance Concrete), a preparation method of the shrinkage reducing agent and a preparation method of a polycarboxylate superplasticizer. Two types of shrinkage reducing monomers are compounded and then polymerized with modified cyclodextrin through an ATRP (Atom Transfer Radical Polymerization) method to generate the shrinkage reducing agent which is adaptive to UHPC (Ultra High Performance Polycarbonate) and has the functions of regulating and controlling surface tension and keeping internal humidity. The preparation process is simple, convenient and easy to control, the cost is low, the product property is stable, on the premise of ensuring the mechanical property of the concrete, the shrinkage rate of the concrete can be stably reduced for a long time, the cracking resistance of the concrete is improved, the durability of the concrete is improved, and the application requirements of UHPC under more complex working conditions are promoted.

Description

Technical Field

[0001] This invention belongs to the field of concrete shrinkage inhibitor technology, specifically relating to a shrinkage-reducing agent for UHPC based on hyperbranched structure grafting and its preparation method. Background Technology

[0002] Ultra-high performance concrete (UHPC), with its ultra-high strength, high toughness, and excellent durability, has become a core building material supporting engineering structures in the "three deep" fields (deep-sea pressure-resistant structures, deep-space landing zone protection facilities, and deep-earth tunnel support systems), demonstrating irreplaceable application value. However, UHPC's ultra-low water-cement ratio and high cementitious material content result in much greater early shrinkage than ordinary concrete, especially autogenous shrinkage, which accounts for approximately 61.3% to 86.5% of total shrinkage. This significantly increases the risk of early cracking in UHPC, provides pathways for harmful substances such as chlorides and sulfates to erode, accelerates the formation of internal defects in the concrete, and increases the risk of steel reinforcement corrosion, ultimately significantly reducing the durability and safety of the structure.

[0003] Currently, methods such as superabsorbent polymers (UHPCs), expanding agents, or shrinkage-reducing agents are commonly used to suppress concrete shrinkage. However, certain limitations still exist. For example, UHPCs are non-water-soluble cross-linked polymers, and their tendency to agglomerate and leave residual pores negatively impacts UHPC performance. Expanding agents struggle to provide sufficient expansion sources in low water-cement ratios, and the degree of expansion is difficult to control precisely. Shrinkage-reducing agents suffer from insufficient shrinkage reduction efficiency due to decreased internal humidity during UHPC hydration and poor compatibility with the UHPC system. Therefore, traditional shrinkage-reducing chemical admixtures not only have limited effectiveness in regulating UHPC performance but also require large dosages, significantly increasing UHPC preparation costs. Furthermore, they significantly affect the compatibility and mechanical properties of chemical admixtures with specific UHPC formulations, greatly limiting the effectiveness and application scenarios of chemical admixtures in UHPCs. Therefore, developing shrinkage-reducing agents that combine the functions of reducing surface tension and maintaining internal humidity can effectively inhibit the early shrinkage of UHPC, reduce the generation of microcracks, extend the service life of the structure, reduce engineering maintenance costs, and promote the application of UHPC in more complex working conditions.

[0004] Patent CN112830704A (publication date: May 25, 2021) discloses an ultra-high performance concrete shrinkage-reducing agent and its preparation method. This invention uses maleic anhydride, polyethylene glycol-based substances, and polypropylene glycol-based substances as main raw materials. After mixing them in a specific molar ratio, the mixture undergoes an esterification reaction at 40-70℃ under the action of a catalyst to generate a compound A solution. Then, a persulfate solution is added dropwise, and the mixture undergoes a polymerization reaction at 50-60℃ for 1-4 hours. Finally, the mixture is neutralized to pH 6-7 to obtain the target shrinkage-reducing agent. The product of this invention is a water-soluble polymer, non-volatile, non-flammable, and has good compatibility with polycarboxylate superplasticizers. It has no significant negative impact on the setting time and later strength of concrete, effectively reducing the risk of cracking.

[0005] Patent CN118755027A (publication date: October 11, 2024) discloses a highly efficient shrinkage-reducing agent and its preparation method. This invention uses unsaturated polyoxyethylene ether macromonomers and low surface tension monomers with polymerization activity as raw materials. Under the action of an initiator and chain transfer agent, the target shrinkage-reducing agent is prepared through a one-step free radical copolymerization reaction at 55-65℃. The preparation process is mild and simple, requiring no high temperature or high pressure conditions. At a low dosage of 0.5% (by weight of cement), the product can reduce the surface tension of the cement paste pore solution by 32.00%-40.00%, with minimal negative impact on the early compressive strength of cement-based materials and beneficial effects on later strength improvement, effectively reducing the generation of microcracks in the matrix.

[0006] However, the shrinkage-reducing agents mentioned in the above patents only achieve surface tension regulation and shrinkage inhibition by introducing low surface tension groups. They do not possess water storage capabilities and fail to achieve a synergistic effect of surface tension regulation and internal humidity retention through molecular structure design. Therefore, their effect on inhibiting the combined effects of self-shrinkage and drying shrinkage in low water-to-binder ratio UHPC systems is limited, making it difficult to address shrinkage and deformation issues during long-term service. In view of this, developing a shrinkage-reducing agent suitable for UHPC that combines surface tension regulation and internal humidity retention is particularly important. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a hyperbranched graft shrinkage reducer adapted to UHPCs, possessing both surface tension regulation and internal humidity retention functions, and its preparation method. This invention innovatively modifies cyclodextrin into a macromolecular initiator, and through ATRP polymerization technology, performs directional hyperbranched graft polymerization of two types of shrinkage reducers. It adds two core steps: precise compounding and regulation of shrinkage reducers and the directional polymerization of modified cyclodextrin. This achieves the synergistic grafting of shrinkage reducer functional groups and water-retaining functional groups onto the main molecular side chains. Through copolymerization, multifunctional side chains with both surface tension regulation and water-retaining capabilities are embedded into the main chain, ultimately obtaining a novel UHPC-adapted shrinkage reducer with both high-efficiency shrinkage reduction and long-lasting moisturizing properties.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows: In a first aspect, the present invention provides a shrinkage reducing agent for UHPC based on hyperbranched graft structure, the chemical structural formula of which is shown below:

[0009] The structural formula for R2 is:

[0010] Where x, y, m, and n are integers representing the number of repeating units in each part of the polymer, x ranges from 10 to 200, y ranges from 1 to 100, m ranges from 8 to 90, and n ranges from 3 to 55; R1 is CH3, C2H5, or C4H9.

[0011] In a second aspect, the present invention provides a method for preparing a shrinkage-reducing agent for UHPC based on hyperbranched structure grafting, comprising the following steps: (1) Esterification reaction of condensed monomer A: Maleic anhydride, polyethylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 80-150℃, reacted for 5-10 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer A. (2) Esterification reaction of condensed monomer B: Maleic anhydride, polypropylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 30-80℃, reacted for 2-8 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer B. (3) Preparation of cyclodextrin-based initiator: Cyclodextrin and reaction solvent were added to a reactor, a magnetic stir bar was placed in the reactor and nitrogen was introduced for protection. The mixture was stirred at room temperature until the cyclodextrin was completely dissolved. An acid-binding agent was added and stirred until evenly dispersed. Then, a mixed solution of acyl halide and reaction solvent was added dropwise. After the addition was completed, the temperature was raised to 35-65℃ and the reaction was carried out for 15-30 hours. After the reaction was completed, the mixture was naturally cooled to room temperature. The supernatant was collected and added dropwise to anhydrous diethyl ether to precipitate a white solid. The solid was filtered and washed with anhydrous ethanol. The solid was then dried under vacuum at 45-65℃ for 10-20 hours to obtain the intermediate product β-CD-(Br) with a degree of substitution n of 3-8. n ; (4) ATRP hyperbranched graft polymerization: The product β-CD-(Br) obtained in step (3) is fed into the reactor. nAfter quickly sealing the main catalyst, evacuate the system and replace the air in the system with nitrogen to ensure an oxygen-free environment. Then add pentamethyldiethylenetriamine and reaction solvent, and stir until complete complexation forms a dark brown color. Continue to add the products obtained in step (1) and / or step (2) and stir until completely dissolved. Then heat to 30-80℃ and react for 15-30 hours. After the reaction is completed, cool naturally to room temperature, purify with alcohol solvent, and vacuum dry at 45-65℃ for 10-20 hours to obtain the suitable UHPC shrinkage reducer.

[0012] Furthermore, the polyethylene glycol substance mentioned in step (1) is polyethylene glycol monomethyl ether or ethylene glycol monoethyl ether; the molar ratio of maleic anhydride to polyethylene glycol substance is 1:1-10; The polypropylene glycol substance mentioned in step (2) is polypropylene glycol monomethyl ether or dipropylene glycol monomethyl ether; the molar ratio of maleic anhydride to polypropylene glycol substance is 1:1-6.

[0013] Furthermore, the catalyst mentioned in steps (1) and (2) is p-toluenesulfonic acid, trifluoromethanesulfonic acid, or sodium bisulfate; the dehydrating agent is toluene, xylene, or cyclohexane.

[0014] Furthermore, the reaction solvent in step (3) is anhydrous N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone, and the mass ratio of the reaction solvent to cyclodextrin is 5-20:1.

[0015] Furthermore, the acid-binding agent in step (3) is triethylamine, tri-n-butylamine, or potassium carbonate; the molar ratio of the acid-binding agent to cyclodextrin is 1-5:1.

[0016] Furthermore, the acyl halide compound mentioned in step (3) is 2-bromoisobutyryl bromide, ethyl 2-bromoisobutyrate, methyl 2-bromoisobutyrate, or tert-butyl 2-bromoisobutyrate; the molar ratio of the acyl halide compound to cyclodextrin is 5-15:1; The mixture of the acyl halide compound and the reaction solvent was added dropwise over 1-4 hours.

[0017] Furthermore, the main catalyst in step (4) is cuprous bromide, cuprous chloride, or cuprous iodide; the main catalyst and the product β-CD-(Br) obtained in step (3) n The molar ratio is 3-15:1.

[0018] Furthermore, the reaction solvent in step (4) is anhydrous N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone; the mass ratio of the reaction solvent to the total reactants in step (4) is 5-15:1; the mass of the total reactants in step (4) is β-CD-(Br). nThe total mass of condensed monomer A and condensed monomer B; the molar ratio of pentamethyldiethylenetriamine to the reaction solvent in step (4) is 5-20:1.

[0019] Furthermore, the alcohol solvent in step (4) is ethanol, methanol, or acetone; the mass ratio of the alcohol solvent to the total reactants in step (4) is 5-20:1; the mass of the total reactants in step (4) is β-CD-(Br). n The total mass of shrinkage monomer A and shrinkage monomer B; In step (4), the condensed monomer A obtained in step (1) and the β-CD-(Br) obtained in step (3) are... n The molar ratio is 5-20:1; In step (4), the product obtained in step (2) is condensed monomer B, and the product obtained in step (3) is β-CD-(Br). n The molar ratio is 5-50:1.

[0020] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention, based on molecular structure design principles, employs a combination of two types of shrinkage-reducing monomers and modified cyclodextrin, polymerized via the ATRP method to create a shrinkage-reducing agent suitable for UHPC (Ultra-High-Pressure PC) that combines surface tension regulation with internal humidity retention. This improves upon traditional shrinkage-reducing agents, which struggle to meet the internal humidity retention requirements of UHPC, leading to shrinkage cracking and uneven strength development during the hardening process due to rapid moisture loss. The molecular design scheme of the shrinkage-reducing agent involved in this invention differs from the structural forms of conventional single-function shrinkage-reducing agents. It innovatively adopts a multifunctional composite modified structure with main and side chains, enabling the prepared specialized shrinkage-reducing agent to simultaneously possess excellent surface tension regulation and internal humidity retention capabilities. The synergistic effect of these two functions effectively enhances the application performance of the shrinkage-reducing agent, broadening the research path for subsequent in-depth development of other novel shrinkage-reducing agents and providing important theoretical basis and technical ideas.

[0021] 2. Existing shrinkage-reducing agents are mostly general-purpose products, lacking molecular structure optimization for the high density, low water-to-binder ratio, and complex composition characteristics of UHPC. This often leads to problems such as poor compatibility with gelling materials, uneven dispersion, short-lasting shrinkage-reducing and moisture-retaining effects, and significant performance degradation in the later stages. This invention, through precise screening of suitable shrinkage-reducing monomers and modified cyclodextrins, and optimization of ATRP polymerization process parameters, directionally introduces highly efficient shrinkage-reducing groups and cyclodextrin water-storing groups into the shrinkage-reducing agent molecular chain. This not only precisely controls the surface tension of the UHPC system and reduces shrinkage stress, but also, through the cyclodextrin cavity structure, forms a stabilizing effect with the internal gelling components of UHPC, improving the dispersibility and compatibility of the shrinkage-reducing agent in the high-density system. This ensures a long-lasting and stable shrinkage-reducing and moisture-retaining effect, meeting the specific system requirements and long-term service requirements of UHPC.

[0022] 3. Existing shrinkage reducing agents are mostly prepared using traditional free radical polymerization processes, which generally suffer from low monomer conversion rates, wide molecular weight distributions of products, and uncontrollable branching structures. This results in large fluctuations in product performance and significant batch-to-batch differences, making it difficult to meet the needs of large-scale industrial production and high-end engineering applications. This invention employs ATRP controlled polymerization technology, using β-CD-(Br) as the polymer. n As a multi-initiation site macromolecular initiator, combined with the CuBr / PMDETA catalytic system, it can precisely control the polymerization reaction rate and molecular chain growth process, realize the efficient conversion of monomers and the directional construction of hyperbranched structures, effectively control the molecular weight distribution and branching degree of the product, and make the prepared shrinkage reducer stable and uniform in performance. Moreover, the preparation process is clear, easy to control, and has good batch-to-batch reproducibility, making it suitable for large-scale industrial continuous production.

[0023] 4. Compared to traditional shrinkage agent synthesis routes, the core steps of this invention, such as cyclodextrin modification, monomer compounding, and ATRP polymerization, are all mature and conventional processes that require no additional special equipment or expensive additives, thus balancing environmental friendliness and production cost control. Furthermore, this synthesis process has no special requirements for production equipment and can be industrialized using existing chemical production facilities, significantly lowering the barriers to industrialization. The synthesized product also boasts advantages such as strong molecular designability, controllable branching degree and molecular weight, and adjustable functional group density, making it adaptable to the preparation needs of UHPC under different ratios and operating conditions. It has significant practical value and broad application prospects.

[0024] 5. Starting from the molecular mechanism, this invention constructs a molecular structure with both surface tension regulation and humidity retention functions through monomer polymerization. On the one hand, through the synergistic effect of two types of shrinkage-reducing monomers, the surface tension of the system is efficiently reduced, thereby reducing shrinkage stress from the source. On the other hand, the water-storing groups of modified cyclodextrin lock in internal moisture, delaying moisture migration and loss, forming a dual mechanism of "shrinkage reduction + moisture retention". Compared with the single mechanism of action of the prior art, the shrinkage reduction and moisture retention effect is more significant, which can greatly improve the crack resistance, durability and long-term mechanical properties of UHPC. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a shrinkage reducing agent for UHPC based on hyperbranched graft structure, the chemical structural formula of which is shown below:

[0027] The structural formula for R2 is:

[0028] Where x, y, m, and n are integers representing the number of repeating units in each part of the polymer, x ranges from 10 to 200, y ranges from 1 to 100, m ranges from 8 to 90, and n ranges from 3 to 55; R1 is CH3, C2H5, or C4H9.

[0029] The above-mentioned method for preparing shrinkage-reducing agents for UHPC based on hyperbranched grafts includes the following steps: (1) Esterification reaction of condensed monomer A: Maleic anhydride, polyethylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 80-150℃, reacted for 5-10 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer A. (2) Esterification reaction of condensed monomer B: Maleic anhydride, polypropylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 30-80℃, reacted for 2-8 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer B. (3) Preparation of cyclodextrin-based initiator: Cyclodextrin and reaction solvent were added to a reactor, a magnetic stir bar was placed in the reactor and nitrogen was introduced for protection. The mixture was stirred at room temperature until the cyclodextrin was completely dissolved. An acid-binding agent was added and stirred until evenly dispersed. Then, a mixed solution of acyl halide and reaction solvent was added dropwise. After the addition was completed, the temperature was raised to 35-65℃ and the reaction was carried out for 15-30 hours. After the reaction was completed, the mixture was naturally cooled to room temperature. The supernatant was collected and added dropwise to anhydrous diethyl ether to precipitate a white solid. The solid was filtered and washed with anhydrous ethanol. The solid was then dried under vacuum at 45-65℃ for 10-20 hours to obtain the intermediate product β-CD-(Br) with a degree of substitution n of 3-8. n ; (4) ATRP hyperbranched graft polymerization: The product β-CD-(Br) obtained in step (3) is fed into the reactor. n After quickly sealing the main catalyst, evacuate the system and replace the air in the system with nitrogen to ensure an oxygen-free environment. Then add pentamethyldiethylenetriamine and reaction solvent, and stir until complete complexation forms a dark brown color. Continue to add the products obtained in step (1) and / or step (2) and stir until completely dissolved. Then heat to 30-80℃ and react for 15-30 hours. After the reaction is completed, cool naturally to room temperature, purify with alcohol solvent, and vacuum dry at 45-65℃ for 10-20 hours to obtain the suitable UHPC shrinkage reducer.

[0030] In step (1), the polyethylene glycol substance is polyethylene glycol monomethyl ether or ethylene glycol monoethyl ether; the molar ratio of maleic anhydride to polyethylene glycol substance is 1:1-10; the catalyst is p-toluenesulfonic acid, trifluoromethanesulfonic acid or sodium bisulfate; and the dehydrating agent is toluene, xylene or cyclohexane.

[0031] In step (2), the polypropylene glycol is polypropylene glycol monomethyl ether or dipropylene glycol monomethyl ether; the molar ratio of maleic anhydride to polypropylene glycol is 1:1-6. The catalyst is p-toluenesulfonic acid, trifluoromethanesulfonic acid or sodium bisulfate; the dehydrating agent is toluene, xylene or cyclohexane.

[0032] In step (3), the reaction solvent is anhydrous N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone, and the mass ratio of the reaction solvent to cyclodextrin is 5-20:1; in step (3), the acid-binding agent is triethylamine, tri-n-butylamine, or potassium carbonate; the molar ratio of the acid-binding agent to cyclodextrin is 1-5:1; the acyl halide is 2-bromoisobutyryl bromide, ethyl 2-bromoisobutyrate, methyl 2-bromoisobutyrate, or tert-butyl 2-bromoisobutyrate; the molar ratio of the acyl halide to cyclodextrin is 5-15:1; wherein, the mixed solution of the acyl halide and the reaction solvent is added dropwise over 1-4 hours.

[0033] In step (4), the main catalyst is cuprous bromide, cuprous chloride, or cuprous iodide; the main catalyst is the same as the product β-CD-(Br) obtained in step (3). n The molar ratio is 3-15:1; the reaction solvent is anhydrous N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone; the mass ratio of the reaction solvent to the total reactants in step (4) is 5-15:1; the molar ratio of pentamethyldiethylenetriamine to the reaction solvent in step (4) is 5-20:1; the alcohol solvent is ethanol, methanol, or acetone; the mass ratio of the alcohol solvent to the total reactants in step (4) is 5-20:1; the mass of the total reactants in step (4) is β-CD-(Br). n The total mass of shrinkage monomer A and shrinkage monomer B.

[0034] In step (4), the condensed monomer A obtained in step (1) and the β-CD-(Br) obtained in step (3) are... n The molar ratio is 5-20:1; in step (4), the condensed monomer B obtained in step (2) and the β-CD-(Br) obtained in step (3) are... n The molar ratio is 5-50:1.

[0035] Example 1 Add 1.31g maleic anhydride, 40g polyethylene glycol monomethyl ether, 1.59g p-toluenesulfonic acid and 50g cyclohexane to a reactor, stir and heat to 125°C, react for 7 hours, filter under reduced pressure after the reaction is completed, and cool to room temperature to obtain condensed monomer A.

[0036] In another reactor, 11.35 g of cyclodextrin and 100 ml of anhydrous N,N-dimethylformamide were added under nitrogen protection and stirred at room temperature until the cyclodextrin was completely dissolved. 15 ml of triethylamine was added and stirred until homogeneous. 8 ml of 2-bromoisobutyryl bromide and 20 ml of anhydrous N,N-dimethylformamide were mixed to prepare solution A. Solution A was added dropwise to the reactor over 3 hours. After the addition was completed, the temperature was raised to 60 °C and the reaction was carried out for 20 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The supernatant was collected and added dropwise to 200 ml of anhydrous diethyl ether to precipitate a white solid. The solid was filtered and washed 5 times with anhydrous ethanol. The solid was then dried under vacuum at 55 °C for 18 hours to constant weight to obtain the cyclodextrin-based initiator.

[0037] In another reactor, 10g of cyclodextrin-based initiator and 8.2g of cuprous bromide were added. After rapid sealing, the system was evacuated and nitrogen was introduced to replace the air in the system to ensure an anaerobic environment. Then, 15ml of pentamethyldiethylenetriamine and 200ml of anhydrous N,N-dimethylformamide were added and stirred until complete complexation to form a dark brown color. 30ml of shrinkage-reducing monomer A was added and stirred until completely dissolved. The temperature was then raised to 80℃ and the reaction was carried out for 25 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, washed and purified five times with anhydrous ethanol, and then vacuum dried at 55℃ for 18 hours to obtain the UHPC-specific shrinkage-reducing agent.

[0038] Example 2 13.23g maleic anhydride, 40g dipropylene glycol monomethyl ether, 2.44g p-toluenesulfonic acid and 50g cyclohexane were added to a reactor, stirred and heated to 50°C, and reacted for 5 hours. After the reaction was completed, the mixture was filtered under reduced pressure and cooled to room temperature to obtain condensed monomer B. In another reactor, 10g of the cyclodextrin-based initiator prepared in Example 1 and 8.2g of cuprous bromide were added. After rapid sealing, the system was evacuated and nitrogen was purged to replace the air in the system to ensure an anaerobic environment. Then, 15ml of pentamethyldiethylenetriamine and 200ml of anhydrous N,N-dimethylformamide were added and stirred until complete complexation to form a dark brown color. 10ml of shrinkage-reducing monomer B was added and stirred until completely dissolved. The temperature was then raised to 80°C and the reaction was carried out for 25 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, washed and purified five times with anhydrous ethanol, and then vacuum dried at 55°C for 18 hours to obtain the UHPC-specific shrinkage-reducing agent.

[0039] Example 3 10g of the cyclodextrin-based initiator prepared in Example 1 and 8.2g of cuprous bromide were added to the reactor. After rapid sealing, the system was evacuated and nitrogen was purged to ensure an oxygen-free environment. Then, 15ml of pentamethyldiethylenetriamine and 200ml of anhydrous N,N-dimethylformamide were added and stirred until complete complexation to form a dark brown color. 20ml of shrinkage monomer A prepared in Example 1 and 5ml of shrinkage monomer B prepared in Example 2 were added and stirred until completely dissolved. The mixture was then heated to 80°C and reacted for 25 hours. After the reaction was completed, it was naturally cooled to room temperature, washed and purified five times with anhydrous ethanol, and then vacuum dried at 55°C for 18 hours to obtain the UHPC-specific shrinkage reducer.

[0040] Comparative Example 1 Add 1.31g maleic anhydride, 40g polyethylene glycol monobutyl ether, 1.59g p-toluenesulfonic acid and 50g cyclohexane to a reactor, stir and heat to 125℃, react for 7 hours, filter under reduced pressure after the reaction is completed, and cool to room temperature to obtain condensed monomer A.

[0041] In another reactor, 10g of the cyclodextrin-based initiator prepared in Example 1 and 8.2g of cuprous bromide were added. After rapid sealing, the system was evacuated and nitrogen was purged to replace the air in the system to ensure an anaerobic environment. Then, 15ml of pentamethyldiethylenetriamine and 200ml of anhydrous N,N-dimethylformamide were added and stirred until complete complexation to form a dark brown color. 30ml of shrinkage-reducing monomer A was added and stirred until completely dissolved. The temperature was then raised to 80°C and reacted for 25 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, washed and purified five times with anhydrous ethanol, and then vacuum dried at 55°C for 18 hours to obtain the UHPC-specific shrinkage-reducing agent.

[0042] The difference between Comparative Example 1 and Example 1 is that in the esterification raw materials, polyethylene glycol monomethyl ether was replaced with polyethylene glycol monobutyl ether.

[0043] Comparative Example 2 In a reactor, 13.23 g of maleic anhydride, 40 g of polypropylene glycol monobutyl ether, 2.44 g of p-toluenesulfonic acid, and 50 g of cyclohexane were added, stirred, and heated to 50 °C for 5 hours. After the reaction, the mixture was filtered under reduced pressure and cooled to room temperature to obtain condensation monomer B. In another reactor, 10 g of the cyclodextrin-based initiator prepared in Example 1 and 8.2 g of cuprous bromide were added. The reactor was quickly sealed and then evacuated and nitrogen was introduced to replace the air in the system to ensure an oxygen-free environment. Then, 15 ml of pentamethyldiethylenetriamine and 200 ml of anhydrous N,N-dimethylformamide were added and stirred until complete complexation formed a dark brown color. 10 ml of condensation monomer B was added and stirred until completely dissolved. The mixture was then heated to 80 °C and reacted for 25 hours. After the reaction, the mixture was naturally cooled to room temperature, washed and purified five times with anhydrous ethanol, and then vacuum dried at 55 °C for 18 hours to obtain the UHPC-specific condensation reducer.

[0044] The difference between Comparative Example 2 and Example 2 is that in the esterification raw materials, dipropylene glycol monomethyl ether is replaced with polypropylene glycol monobutyl ether.

[0045] Comparative Example 3 A commercially available common shrinkage reducing agent was used as Comparative Example 3, with a solid content of 40%.

[0046] Test result comparison: 1. Surface tension test Surface tension was tested using a BZY series fully automatic surface tension meter. Pore solutions were extracted from cement pastes containing different amounts of shrinkage-reducing agent (based on cement mass) from each experimental example, and surface tension was tested. A certain amount of cement, water, and 0.1%, 0.2%, 0.5%, 1%, 2%, and 3% of the shrinkage-reducing agent from each experimental example were mixed and manually stirred for 5 minutes to prepare cement pastes. Pore solutions were extracted from the cement pastes and filtered using a 0.22 μm pore size filter membrane. The test results are shown in Table 1.

[0047] Table 1 Surface tension test results

[0048] According to the test results in Table 1, the shrinkage reducing agents prepared in Examples 1-3 are more effective at reducing surface tension than those in Comparative Example 3. Furthermore, comparing the data from Examples 1-2 with those from Comparative Examples 1-2 shows that, at the same concentration, the shrinkage reducing monomer obtained by esterification of maleic anhydride and polyethylene glycol monomethyl ether has a better surface tension reducing performance than the shrinkage reducing monomer obtained by esterification of maleic anhydride and polyethylene glycol monobutyl ether; and the shrinkage reducing monomer obtained by esterification of maleic anhydride and dipropylene glycol monomethyl ether has a better surface tension reducing performance than the shrinkage reducing monomer obtained by esterification of maleic anhydride and polypropylene glycol monobutyl ether.

[0049] 2. Compressive strength and flexural strength tests The compressive strength and flexural strength tests were conducted in accordance with the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019). The compressive strength test specimens were standard cubes measuring 100mm × 100mm × 100mm. After pouring and curing, compressive strength tests were conducted after 7 days, 28 days, and 60 days of curing, with a loading rate of 2.4 kN / s. The flexural strength test specimens were prisms measuring 40mm × 40mm × 160mm. After pouring and curing, flexural strength tests were conducted after 7 days, 28 days, and 60 days of curing, with a loading rate of 50 N / s. The test results are shown in Table 2. The shrinkage-reducing agent content in the concrete was 0.5% (based on cement mass).

[0050] Table 2. Effects of shrinkage reducing agents on compressive and flexural strength.

[0051] As can be seen from the test results in Table 2, by comparing the data of Examples 1-2 with those of Comparative Examples 1-2, the compressive strength of Example 1 is slightly lower than that of Comparative Example 1, and the compressive strength and flexural strength of Example 2 are slightly lower than those of Comparative Example 2. However, the shrinkage reducing agent prepared in Example 3 has the best compressive strength and flexural strength in the 6 groups of experiments. Among them, the compressive strength of UHPC after curing for 28 days reaches 142.43 MPa and the flexural strength reaches 19.1 MPa.

[0052] 3. Self-shrinkage and drying shrinkage tests According to the "Standard for Test Methods of Long-Term Performance and Durability of Concrete" GB / T50082-2024, the autogenous shrinkage of mortar was tested using a corrugated pipe autogenous shrinkage tester. The corrugated pipe was 420 mm long and 80 mm in diameter. The corrugated pipe specimen was placed horizontally on the tester, and the test period was 28 days. The drying shrinkage test specimens were prepared with dimensions of 25 mm × 25 mm × 280 mm. After curing in a curing room at an ambient temperature of 20℃ ± 1℃ for 48 hours, the specimens were removed, and the initial reading was measured using a length comparator. After measuring the initial length, the specimens were placed in a drying shrinkage curing chamber for curing, and the length was measured again at the specified age. The test results are shown in Table 3. The shrinkage-reducing agent dosage in the concrete was 0.5% (based on cement mass).

[0053] Table 3. Results of Shrinkage Performance Tests for Shrinkage Reducing Agents

[0054] As shown in Table 3, the shrinkage reduction effect of UHPC incorporated with the shrinkage reduction agent prepared according to the present invention is as follows: the maximum reduction in self-shrinkage at 3d and 7d exceeds 70% (70.73% and 73.82% of Example 3), and the reduction in self-shrinkage at 28d reaches more than 45% (48.97% of Example 3); the maximum reduction in drying shrinkage at 7d and 28d exceeds 50% (54.83% and 61.13% of Example 3), and the reduction in drying shrinkage at 60d reaches more than 35% (38.62% of Example 3). All of these results are superior to the commercially available shrinkage reduction agent in Comparative Example 3, demonstrating excellent shrinkage reduction effect. Comparing the data from Examples 1-2 and Comparative Examples 1-2, it can be seen that the shrinkage-reducing monomer obtained by esterification of maleic anhydride with polyethylene glycol monomethyl ether has better shrinkage-reducing properties than the shrinkage-reducing monomer obtained by esterification of maleic anhydride with polyethylene glycol monobutyl ether; and the shrinkage-reducing monomer obtained by esterification of maleic anhydride with dipropylene glycol monomethyl ether has better shrinkage-reducing properties than the shrinkage-reducing monomer obtained by esterification of maleic anhydride with polyethylene glycol monobutyl ether.

[0055] 4. UHPC internal relative humidity test The relative humidity inside ultra-high performance concrete (UHPC) was tested using an RH-5A humidity sensing system. The well-mixed UHPC mixture was poured into a 100mm×100mm×100mm triple mold. After compaction and leveling, an acrylic tube with an inner diameter of 11mm was embedded inside the mixture, and the tube opening was sealed with a rubber stopper. The mold was placed in a constant temperature curing chamber for 1-2 days, then demolded. The rubber stopper was removed, and a humidity sensor was inserted to continuously monitor the relative humidity changes in the central area inside the UHPC. The test results are shown in Table 4. The shrinkage-reducing agent content in the concrete was 0.5% (based on cement mass).

[0056] Table 4. Test results of the shrinkage reducer's performance in maintaining relative humidity inside the UHPC

[0057] The test results in Table 4 show that the overall trend of the samples is that the internal humidity gradually decreases with increasing time. Compared with Comparative Example 3, the shrinkage reducing agents prepared in Examples 1-3 have a better ability to maintain the internal relative humidity of UHPC. Among them, Example 3 shows the best ability to maintain the internal relative humidity of UHPC. This is mainly because when the internal humidity is high in the early stage, the water-absorbing groups on the molecular chain will store some water. As cement hydration continues, the internal humidity of UHPC begins to gradually decrease, and the water-absorbing groups release water to maintain its internal humidity environment. By comparing the data of Examples 1-2 and Comparative Examples 1-2, it can be seen that the shrinkage reducing monomer obtained by esterification of maleic anhydride and polyethylene glycol monomethyl ether has better water retention performance than the shrinkage reducing monomer obtained by esterification of maleic anhydride and polyethylene glycol monobutyl ether; the shrinkage reducing monomer obtained by esterification of maleic anhydride and dipropylene glycol monomethyl ether has better water retention performance than the shrinkage reducing monomer obtained by esterification of maleic anhydride and polypropylene glycol monobutyl ether.

[0058] In summary, this invention utilizes a combination of two types of shrinkage-reducing monomers, which are then polymerized with modified cyclodextrin via the ATRP method to create a shrinkage-reducing agent suitable for UHPC that combines surface tension regulation with the function of maintaining internal humidity. The preparation process of this invention is simple and easy to control, cost-effective, and produces a stable product. While ensuring the mechanical properties of concrete, it can stably reduce concrete shrinkage, improve concrete crack resistance, and enhance concrete durability over a long period, which is beneficial for promoting the application of UHPC in more complex working conditions.

[0059] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made using the present invention specification, or any direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A shrinkage reducing agent for UHPC based on hyperbranched structure grafting, characterized in that, Its chemical structural formula is shown below: The structural formula for R2 is: Where x, y, m, and n are integers representing the number of repeating units in each part of the polymer, x ranges from 10 to 200, y ranges from 1 to 100, m ranges from 8 to 90, and n ranges from 3 to 55; R1 is CH3, C2H5, or C4H9.

2. A method for preparing a shrinkage-reducing agent for UHPC based on hyperbranched structure grafting as described in claim 1, characterized in that, Includes the following steps: (1) Esterification reaction of condensed monomer A: Maleic anhydride, polyethylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 80-150℃, reacted for 5-10 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer A. (2) Esterification reaction of condensed monomer B: Maleic anhydride, polypropylene glycol, catalyst and dehydrating agent are added to the reactor, stirred and heated to 30-80℃, reacted for 2-8 hours, and after the reaction is completed, vacuum filtration is performed and cooled to room temperature to obtain condensed monomer B. (3) Preparation of cyclodextrin-based initiator: Cyclodextrin and reaction solvent were added to a reactor, a magnetic stir bar was placed in the reactor and nitrogen was introduced for protection. The mixture was stirred at room temperature until the cyclodextrin was completely dissolved. An acid-binding agent was added and stirred until evenly dispersed. Then, a mixed solution of acyl halide and reaction solvent was added dropwise. After the addition was completed, the temperature was raised to 35-65℃ and the reaction was carried out for 15-30 hours. After the reaction was completed, the mixture was naturally cooled to room temperature. The supernatant was collected and added dropwise to anhydrous diethyl ether to precipitate a white solid. The solid was filtered and washed with anhydrous ethanol. The solid was then dried under vacuum at 45-65℃ for 10-20 hours to obtain the intermediate product β-CD-(Br) with a degree of substitution n of 3-8. n ; (4) ATRP hyperbranched graft polymerization: The product β-CD-(Br) obtained in step (3) is fed into the reactor. n After quickly sealing the main catalyst, evacuate the system and replace the air in the system with nitrogen to ensure an oxygen-free environment. Then add pentamethyldiethylenetriamine and reaction solvent, and stir until complete complexation forms a dark brown color. Continue to add the products obtained in step (1) and / or step (2) and stir until completely dissolved. Then heat to 30-80℃ and react for 15-30 hours. After the reaction is completed, cool naturally to room temperature, purify with alcohol solvent, and vacuum dry at 45-65℃ for 10-20 hours to obtain the suitable UHPC shrinkage reducer.

3. The preparation method according to claim 2, characterized in that, The polyethylene glycol substance mentioned in step (1) is polyethylene glycol monomethyl ether or ethylene glycol monoethyl ether; the molar ratio of maleic anhydride to polyethylene glycol substance is 1:1-10; The polypropylene glycol substance mentioned in step (2) is polypropylene glycol monomethyl ether or dipropylene glycol monomethyl ether; the molar ratio of maleic anhydride to polypropylene glycol substance is 1:1-6.

4. The preparation method according to claim 2, characterized in that, The catalysts mentioned in steps (1) and (2) are p-toluenesulfonic acid, trifluoromethanesulfonic acid, or sodium bisulfate; the dehydrating agent is toluene, xylene, or cyclohexane.

5. The preparation method according to claim 2, characterized in that, The reaction solvent in step (3) is anhydrous N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone, and the mass ratio of the reaction solvent to cyclodextrin is 5-20:

1.

6. The preparation method according to claim 2, characterized in that, The acid-binding agent mentioned in step (3) is triethylamine, tri-n-butylamine or potassium carbonate; the molar ratio of the acid-binding agent to cyclodextrin is 1-5:

1.

7. The preparation method according to claim 2, characterized in that, The acyl halide compound mentioned in step (3) is 2-bromoisobutyryl bromide, ethyl 2-bromoisobutyrate, methyl 2-bromoisobutyrate, or tert-butyl 2-bromoisobutyrate; the molar ratio of the acyl halide compound to cyclodextrin is 5-15:1; The mixture of the acyl halide compound and the reaction solvent was added dropwise over 1-4 hours.

8. The preparation method according to claim 2, characterized in that, The main catalyst mentioned in step (4) is cuprous bromide, cuprous chloride, or cuprous iodide; the main catalyst is the same as the product β-CD-(Br) obtained in step (3). n The molar ratio is 3-15:

1.

9. The preparation method according to claim 2, characterized in that, The reaction solvent in step (4) is anhydrous N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone; the mass ratio of the reaction solvent to the total reactants in step (4) is 5-15:1; the mass of the total reactants in step (4) is β-CD-(Br). n The total mass of shrinkage monomer A and shrinkage monomer B; In step (4), the molar ratio of pentamethyldiethylenetriamine to the reaction solvent is 5-20:

1.

10. The preparation method according to claim 2, characterized in that, The alcohol solvent in step (4) is ethanol, methanol, or acetone; the mass ratio of the alcohol solvent to the total reactants in step (4) is 5-20:1; the mass of the total reactants in step (4) is β-CD-(Br). n The total mass of shrinkage monomer A and shrinkage monomer B; In step (4), the condensed monomer A obtained in step (1) and the β-CD-(Br) obtained in step (3) are... n The molar ratio is 5-20:1; In step (4), the product obtained in step (2) is condensed monomer B, and the product obtained in step (3) is β-CD-(Br). n The molar ratio is 5-50:1.

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